Process of purifying and dewaxing mineral oils



Y 29, 1936. G. J. STREZYNSKI 2,066,164

PROCESS OF PURIFYING AND DEWAXING MINERAL OILS Filed June 27, 1935 2 Sheets-Sheet 2 //VVE/V 70/? MEG/55$" @a/ye 6 7 5/35 wfzim Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE Application June 27, 1935, Serial No. 28,655

7 Claims.

In the refining of parafiin base petroleums (ineluding mixed base petroleums) for the production of lubricating oil, several procedures are required. It is necessary to remove impurities and 3 compounds which are detrimental to the lubricating qualities. It is also necessary to remove all waxes down to certain temperatures, usually between F. and 20 F., in order to prevent the oil congealing during cold weather. I

The impurities are usually removed by chemical action with sulfuric acid. The reaction of H2SO4'Withthe impurities forms a so-called 'acid' sludge which,. beingconsiderably heavier than the oil, precipitates and is removable by gravity or by centrifugal separation.

The waxy compounds require removal by two difierent methods, the necessity for which arises from the difierent character of the waxy compounds, which may be grouped mtg two general classes, 'one, the so-called amorpho waxes, having a buttery structure, and the other more of a,

crystalline structure, forming granules, flakes or needles, or even, when rapidly crystallized,

massed into a semi-solid jelly-like material. Normally the. amorphous waxes are heavier than ,the crystalline waxes, the latter carrying considerablevoil. Due to the small gravity diiference between crystalline wax and the oil and to the' spongy structure of the crystals, they are difficult to separate by gravity or centrifugal force and such procedure is usually considered impracticable, but they are readily filtered, and the resultant cakes of wax, when allowed to lie in pans, will drain themselves of any remainingoil. The amorphous waxes, being of more homogeneous structure andconsisting of fine particles, cannot be pressed or sweated, but, because of their greater concentration'and higher gravity, are separablei by gravityor centrifugal force.

" Usually, therefore, parailiri base oils are purified' and dewaxed by a multiple step process. In the dewaxing treatments the oils are first distilled to about 30% bottoms. Theportion distilled over carries most of the crystallinewaxes.

The 30% residue contains most of the amorphous.

waxes. A fraction of the overhead is then refrig'erated, pressed and sweated for. the removal of the crystalline wax, called parafiin. The bot-' tom are acid-treated, refrigerated and centrifuged for the removal of amorphous wax, called petrolatum. w

My invention comprises a process for purify.- ing the' oil and removing both kinds of waxes in one unitary process. I v

Itgjhas been proposed, after distilling oi! only a small fraction of light constituents, to subject the oil, in a batch treatment, successively to refrigeration and addition of acid (in the order specified or 'in the reverse order) and then by gravity settle out the resultant mixture of acid sludge and waxes. In such a process, the resultant product separates into an upper layer of clear dewaxed oil and a lower black layer of 'waxy acid sludge; but it also exhibits an intermediate phase, nearly white, between the sludge 1 and the clear oil. The line of demarcation between the clear oil and this intermediate fioc- V culent layer is, in most cases, very indistinct, the

two phases gradually merging together. I have found thatthis intermediate phase has a particularly high viscosity index number. Its in clusion in the separated clear ofl considerably 1 increases the viscosity index number of the whole Oil; The gravity of this intermediate phase I have 20 found to be so close to that of the clear and entirely dewaxed oil that its separation therefrom, 1 either by. gravity or by ordinary centrifuges, is impracticable. In gravity settlement so large a percentage of the oil must be carried oif with the 25 sludge that there is obtained a poor percentage yield of oil for a given amount of crude. In centrifugal treatment, wherein the oil and sludge discharges in continuous streams from the inner and outer zones, respectively, of the separating space of the bowl, it was found that the'inter-v mediate phase would accumulate in the vessel 1 until it would discharge with the clear oil, which resulted in a poor pour point. and waxy oil.

If oil containing only amorphous'wax could be 1 treated in accordance with the gravity settling method above described, it,is possible that a more satisfactory product would be secured; but parafe fin base oils always contain, it is believed, wax

in both forms (whether present assuchin the '4 original crude or potentially present therein 80 as to be necessarily produced by refrigeration): and therefore such process is believed to possess no commercial value, v

I have devised a process whereby the oil V (which is preferably the crude oil with or without preliminary'lightdistillation, but may be along I residuum containing all the lubricating -fractions) may be both purified and completely dewaxed in a unitary process which may be carried out continuously and-wherein the final separating step may be successfullyeil'ected. by means-of centrifugal force. :In stating that the oilis' completely dewaxed, it will be understood that what is meant is that the waxiscompletely removed I down to the temperature of the pour point. de-.

sired;'in other words, that all such wax is pre-- cipitated and that all the precipitated wax is pour point of F., viscosity index 86 and via-- cosity 67 at 210 F.

To facilitate a description of the process, I illustrate various means be carried out.

Fig. 1 is a flow sheet showing the entire apparatus.

Fig. 2 is a vertical section through apreferred 7 'form of centrifuge.

Fig. 3 is asection, on a larger scale and in more detail, of a partof the centrifuge of Fig. 2.

. Figs. 4 and-5 are vertical sectional views of modified forms of centrifuges in which it is pos sible to carry out the process.

As above stated, it ispreferred to process the I crude oil. If .it 06 tains water, it should be dehydrated; nprefera ly, however, by a method which involves as little removal as practicable of light oil fractions. It is preferred to'dewax the 'crude, since if all fractions except those desired for lubrication are distilled off, it is necessary to make'a very considerable addition of a lightoil fraction, such as naphtha, to the oil in order to .decrease the specific gravity of the oil relatively to-the wax, with the former of which the diluent has a preferential'solve'nt action. Even starting with the crude, it is necessary, in the most desirable embodiment of the invention, to dilute with a light. oil fraction. starting with a crude 00h taining about eight per cent. of wax,-it is desirable to add about '19 parts of the diluent to, 100

. parts of the crude. The proportion of diluent that should beadded-is jquite variable with differentoils. -I have found, however, that it is highlyfdesirable to add to the crude a light'hy drocarbon' oil in such amount that there -will form, in the chilledand acid treated oil, an acid sludge having a massbetween 15 and 30 per cent. or? the entire mass of' the treated, oil under a force'of 6000 times that of gravity. Preferably this percentage shouldbe between 20 and 25 per cent.

. Separate streams of crudeand dlluentrain the chilled. The cooling procedure in specified proportions, are delivered to a "blending tank Ill, whence the oil is pumped through a chilling device u, b: chiller'f, which comprises a long cylinder through the type known as a, ribbon which extends a rotatable core-provided with'a helical conveyor wing. Insucha'chiller the oil,

is maintained in motion or agitation and spread over a considerable surface and 181F123?! rapidly a chiller may be properly designated "shock chilling",-al-

though it will .be understood that'chillingat a:

' slower rate is permissible, although not desirable.

The temperature to .which the bills cooled will .vary with the pour test'desiredfor the finished .011. If such flnished'oil is desired to' flY D0111.

' test of 20' F, chilling to about -10- 1".ls necessary. If the finished'oil isdesired to'have a pour test of 0 F chilling to about -35 F. is necessary. The degree of chilling may varyfrom '0 F.

to -'5,0 I"., dependent on the pour test .The chilling operation dllcribod will w'ccipir whereby the process may s aoeaioi tate'all wax. By means of aypump It, the"v mixture of 011 and wax is conveyed to a mixer M, which may be a centrifugal pump. Into the oil line leading to the mixer I4 is conveyed, through a pump l3, a stream of concentrated sulfuric acidlsay 98% H2804) The amount of acid so conveyed may be quite variable, but I prefer to use a quantity of acid-substantially in excess of that required for thereaction, since this much enhances the eihciency of the process and involves no substantial waste of acid; nearly all of it being'recoverable, and the-bulk .oi the acid 'recovered being concentrated acid adapted for re- .use in the process. While the percentage of acid may be varied within limits at the discretion of the operator, the necessary percentage of acid will vary with the desired pour test of the flnished oil. Thus. in producing 20 F. pour test oil, a desirable addition' of acid is about 12 to 14 pounds per barrel, or about 2%%; while in producing 0 F. pour test oil, a desirable addition of acid is about 24 to 28 poundaor about 5%.

It isimportant that the acid that is added should not freeze. To avoid freezing, I prefer that the temperature of the added acid should be nearly or quite F., although this temperature may be varied within considerable limits, say

Y between 110? and 1?. Another advantage of 'addinghot acid is that it speeds the reaction. The addition of the acid necessarily raises the temperature of the mixture, for which reason the chilling should be carried to a temperature below that which would otherwise be necessary. In the examples given above, themixture is raised in temperature, by the addition of the acid, from .16 F. to -6'.F. or from 35 F. to '25 F. It is preferred not to complete the mixing in the pump it but to run it through an additional mixer l5, which may be aseries of centrifugal pumps. The acid reacts with the oil and .wax .and forms a mixture of waxyacid sludge and oil containing wax in'ilne suspension but otherwise purified.

The mixture is then conveyed to a centrifuge I which is specially designed tb so act upon'the mixture as to enable the-recovery'df completely .dewaxed oil. -A preferredconstruction of centrifuge isshown in Figs. 2 and 3 and will now be described in detail.

a is the shell of a bowl-having a. top b and containing a tubular feed shaft or distributor c and a set oi?= separating discsd. 'Ihe'feed to the ,bowl is through tube eand feed shaft ci'nto .the separating 'cham' her I of the bowl. The for oil is at! and that ifor outlet sludge is-at a.

seat 7' against which seats a floating conical valve In constituting the outerend of a radially extending hollow cylindrical body 1. Through the apex of the cone k is a small 'oriilce m. Small lugs 0 on the outside of the valve body :rcentral- 'ize it inthe tube p'which surrounds, protects and guides it. Supported and guided-by a head se cured to and fitting the inner end of the tube 9 is a plug 0 that nearly fllls,.but does not touch, the inside of the valve bowl a wall q forms, with the bowl-bottom, an annular chamber which,

divided into as 'many compartments a as there wax and oil separating body 2:. Underneath the by mdiei' imtitiom, a. '10

described. in theside of, each guide tube-p is a slot t providing. communication between chamber sand the annular space between the valve body a: and tube 9. The liquid flows from In the bowl wall around the port 1 is 'a.' valve that part of said annular space communicating with the interior of the bowl into chamber sand flows out of chamber 8 into that part of said annular space communicating with the interior of f the hollow valve body 2:. The cross pin it in the plug 11 limits the movement of the valve body m away from its seat.

With the use of the plug '0 only a small quantity 5 of liquid needs to be drained from the chamber 8 in order to empty it of a substantial proportion of liquid.

In operation, oil that has been so chilled that the acid sludge has been thrown out of solution is fed through the tube e and tubular shaft to the interior of the bowL-where itenters the'spaces between the discs 6. At .the same time oil enters each of the guide tubes pand causes the corresponding valve r-toi float toward the center until stopped by the pin u. Oil temporarily escapes through the port -g, but oi. quick-- ly fllls the tube. 11 and space 8 and flows into and fills the valve :c, which then moves'outward and closes the port g.

Between the discsd the oil and wax are'sepa rated by centrifugal force; The dewaxed oil escapes from the bowl at f and the acid sludge collects in a layer against the bowl wall. As soon as this'layer is thick enough to cover the end of the tube 9 it stops the flow of oilithereinto. The

continuing escape of oil from the valve through 1 the orifice m soon so lightens thevalve that it floats radially inward in the body of oil in which it is immersed and opens the port g,- allowing sludge to be discharged" therethrough until the thickness of the sludgelayer intlie bowl 'is-so reduced that it uncovers the end of tube '12 and the flow of oil from the interior of the bowl into tube p is then resumed.- Said oil quicklyreplaces that which had escaped and'fllls the valve so that it again closes. This cycle of operations is repeated indeflnitely.

While the action of this valve is actually intermittent, the open intervals and the closed intervals a're'both of such short duration that the resultant is substantially-equivalent'to a contin uous discharge of wax as fast as it separates from the oil;

"I'heoil-that operates the'valve is held-in the chambers s for a time sufllciently long-to effect therein a clean separation of its contained wax.

before the. oil, reaches the interior of the valve body. ,The clean oil can flow through the orifice 11': as fast as desired.

In the operation asabove described-the oil that flows from the separating space of the bowl into the valve body axis only that part of the oil which, during the separation,-is in a narrow annuiar zone" adjacent the. peripheral zone of acid sludge. I have found thatit is only this zone of oil that contains wax in fine suspension. The remaining and major part (inner zone) of the body of oil that is at any 1 given time in the separating chamber of the bowl contains substantially no suspended wax, so that the ,o discharged through the outlet. I is substantiallycompletely dewaxed as well as otherwise purified:

It is not necessary'to provide special separatingchaimbers 8. All the oil within and near to'the peripheral layer of accumulated sludge around .the edge of chamber 1) may flow into theinterior of the valve body .12 and may be discharged, with the sludge, through the port q. 'I'he'main advantage of separating out the waxbefore admitting the oil to the valve-chamber is to avoid danger 'of clogging of the valve outlet bylflne wax partiacid treated 'cl es. The oil admitted into the valve whether or not wax is previously separated there- 1 from in chambers s, comprises a very minor proportion of the entire separated voidineof oil and may be subsequently separated from the acid sludge by a process which need not be described,

since it is nirpart of the present invention.

The process isr-not dependent for its execution upon the use of ;a centrifuge with floating valve as above described. The use, however, of a known three-way dischargebowl with the conventional discharge dams gives unsatisfactory results.v when itwas attempted to regulate these dams to corresponding gravities, it was found that there was not enough gravity diiferential and that the gravity differential was not stable enough to establish the proper diameter, which resulted in" losing'purifledand dew'axed oil over the intermediate dams or iiot obtaining enough discharge from the intermediate dams toeflect a complete removal of the intermediate phase. I then conceived the idea of providing discharges over any gravity controlled discharges, like dams,'but to have the intermediate discharge. restricted to a certain limited proportion by means of restricted outlets. The restriction must be of suchcharacter that the intermediate discharge varies from '5 to of thfietfltfil feed. The construction is illustrated in Fig. 4, wherein. is the discharge for the purified dewaxed oil, 20 the discharge'for "3, with a floatingj-valve 1:, operating as hereinbefore described, but wherein the intermediat e phase discharge-is located independent .ofthe valve but leading fromthe; zone detemiined by the edge and somewhat iiiside that diameter. In this ,con

struction the g intermediate phase -discharges through the restricted holes II, the diameter of the top disc 52 being somewhat inside the edge of the tube p. 1! represents the zone of sludge-free but only partly dewaxed .oil.

- The process is not dependent for its execution upon acid trea ting andchilling in the manner and in the order nescribed. Thus, if the process is applied, for example, to a long residuum, wherein it is necessary to use a much larger proportion of diluent, it is practicable, and sometimes advantag eous, to addthe acid to the stock to-be treated at room temperature or, say, at any temperature between 20. F. .and 80? F. to chill only the diluent L and to then add: the chilled diluent tothe acid I is practicable iithe proportion or tively high;

I do not herein claim separate and apartffrom the process as a whole, certain novel features of the above described process, such as the regulatreatedstock. =1'I'his modification of the;

diluent isrela '1 tion of the temperature of refrigerationand of the I acid so as to preve t freezing of the acid and obtain a maximumdegree of reaction, as set forth in an application mes; by the 'June. 27, 1935, Serial No.'28,656, and the regulation of the proportion of diluent added to give a proportion of sludge with: in certain limits,yas set-forth in an application filed jointly by George M; Ffau and myself July 25, 1935, Serial'No. 33,073. Hz

Nor do I claim herein the separator construction's-herein described, since, while they are especially adapted to carry out my process, they are or may be used, to advantage in other p; and, moreover, it is possible to practice the present process in separators of other constructions: The separator shown in Figs. 2 and-3 is disclosed in a patent issued to me December 8, 1935, No, 2,022,816. o 1 f What -I claim and desire'to protect by Letters Patent is:

1. The process oi substantially completely dewaxing mineral oil that contains both amorphous and crystalline waxes and which has been chilled to a temperature below o F. and reacted with sulfuric acid, which comprises subjecting the resultant mixture 01' oil and sludge to centrii'ugal force to thereby separate thesame into a peripheral zone of -acid sludge containing the major part 20 ofthe. wax, an inner zone of purified dewaxed oil and an intermediate zone oi otherwise purified I oil but containingfwax in suspension, and discharging the purified dewaxed' oilseparately from the remaining separated constituents. 25. "2. The process of substantially completely 'de waxing'mineraI oil which has been chilled to a wax-precipitating temperature and reacted; with sulfuric acid, which comprises continuously flow-- ing the resultant chilled mixture. of oil and acid sludge-into a revolving-separator bowl and thereiin separating the same into three phases, namely, a peripheral sludge phase, an inner pureoil phase and an intermediate phase comprising oil containi ng-wax in suspension, separately discharging the three phases'and so controlling the outlet lor--. the intermediate phaseas to limit the ratio oidlscharge of such-phase-to the total discharge to less'th'an twenty percent. Y e 3. The process of substantially completely dewaxing. mineral oil which has been chilled-to a wax-precipitating temperature and reacted with \v sulfuric acid, which comprises continuously flowing the resultant-chilled'mixture of oil and acid sludge into a revolving separator bowl and there- 45 in-separatln'gthe same into three phases, namely, a peripheral sludge phase, an inner pure oil phase and an intermediate phase comprisin'g'oil containing wax in suspension, continuously discharging the pure-oil phase, alternately accumu a ing- 50 and discharging the sludge phase, cuttlowingthe intermediate sludge phase from the separator space or 'the bowl during, discharge and accumulationeof. the sludge'phase, and temporarily ar! resting said outflow after a definite accumulation of the'sludge phase. 1 1

65 4. The process or substantially completely dewaxing mineraloil which has been chilled to a."

' wax-precipitating tempqrature and with. sulfuric acid, which-comprises continuouslyflowin separating the. same into'three phases, namely,- a peripheral, sludge phase, an inner pure oil phase and-(an intermediate phase comprising oil coning the pure oil phase, alternately accumulating and discharging j the sludge phase, alternately outflowing the intermediate from the separatingv space 01' the bowl and arresting said out flow, outflowing the intermediate phase while the sludge phase is accumulating, arresting the outw f e intermediate phase after a l mm amount: of the sludge has b to thereby graduallydiminish ing the resultant chilled mixtureoi oil and acid sludge into a revolving separator bowl and therej talning wax in suspension,continuously discharg-- fiilldf about;

starting the discharge or the sludge phase after the outilow otthe intermediate phase has been arrest d, and starting the outflow or the intermediate phase during the discharge of the sludge Phase. v

. 5'. The process or substantially completely demineral oil which hasbeen chilled'to a wax-precipitating temperature and. reacted with sulfuric acid, which comprises continuously flowing the resultant-chilled mixture of oil and acid sludge into a revolving separator bowl and there in separating thesame into a peripheral zone of waxy acid sludge, an inner zone of purified dewaxedoll and an intermediatezone of all containing wax in" suspension, discharging from theseparating space of the bowl thep'urihed dewaxed oil, separately outflowing' from the separating space of the bowl oil containing wax in suspension' untll a layer of sludge of predetermined, thick ness'accumulates on the bowl ll and then arresting said outflow, intermittently discharging sludge from said layer to allow intermittent resumption or said outilowjo'r oil containing waxin suspension, continuously'discharge i s f outflbw'ed from "the separating space 01' the bowl, and controlling said intermittent discharge of sludge .by the speciiied intermittent outflow and continuous discharge of the last named oil. 6. The process of substantially completely dewaxing mineral oil which has been chilledto a wax-precipitating temperature-and reacted with sulfuric acid, which comprises continuously flow through. an outlet 'in the peripheral wall oi the howl, intermittently outilowijng from the separating space of the bowl, oil containing wax 'in suspensioninto a'sepa'rate floating chamber in said. bowl, said chamber with its contained oil being intermittently. increased ,in weight by said flow of t r nt o sly d s harslnrit oil containing wax in suspensionirom ald cham controllingthe rpp'ening and closing oi said peripheral outlet by'moving said chamber, by vary ingits weight asspeciiled, into andout'oi position v to close said outlet. 5 '1 he p o s nur ncand substantial y. completely dewaxing' oil which comprises. addingthereto a hydrocarbon oil diluent in such amount that in the subsequent} below-defined treatingsteps the waxy acid sludge will have. a

mass-edual toi5 to 30% oitliemass oi the'treated oil before separation, thediluted oil to a temperature 0 1!. to precipitate the wax,

reacting' thechillcd mixture 0! oil-and wax with sulfuric acid; subjecting the chilled acidetreated mixture to centriiu'galiorce to therebyseparate thes'ame into aj'peripheral lame. of sludge,'- an.in .ner zone oi purified dewaxed oil and an intermediate-acne oi oil eontaining wax in suspension discha gin the n medewaxed 'oil: sena- 7o rately irom the remaining constituents.-

jonoaos J'." l

m the bowl the oil that has intermittently 25 I its and- 59 

